One problem related to manifold/header/muffler/tail pipe has been reported for the 2006 Lexus IS250. The most recently reported issues are listed below.
I purchased a 2006 is 250 in October, 2005. The vehicle has been driven for 2,500 miles. After the engine warms up, smoke and a burned smell come from the engine compartment. The first time I brought the problem to the dealers attention I was told that everything was normal. I brought the vehicle in a second time and it was discovered that oil was leaking from the passenger's side valve cover onto the hot exhaust manifold causing the oil to smoke and burn. The vehicle is now at the dealers service department and I am being told that they do not know how to fix the problem and that they have no parts to use for replacement since the design is so new. The problem is related to the high oil pressure maintained by the engine according to the dealer. The engine is covered with plastic panels and I have advised the dealer that continual leakage of oil onto the hot exhaust manifold with a plastic cover on top of the engine could result in an engine fire. Smoke is visible from the engine compartment when the engine is running.